As a method for forming an amorphous silicon film or polysilicon film used in production of a solar battery, a thermal CVD (Chemical Vapor Deposition) method using a monosilane or disilane gas, plasma CVD method or optical CVD method has heretofore been employed. In general, the thermal CVD method (refer to J. Vac. Sci. Technology., Vol. 14, p. 1082 (1977)) is widely used to form the polysilicon film, and the plasma CVD method (refer to Solid State Com., Vol. 17, p. 1193 (1975)) is widely used to form the amorphous silicon film.
However, the formation of the silicon films by these CVD methods has problems that since a gas phase reaction is used, the contamination of equipment and/or production of foreign materials are/is caused by by-production of silicon particles in the gas phase, thereby lowering a production yield, that since the raw material is in gaseous form, it is difficult to form a silicon film having a uniform film thickness on a substrate having an uneven surface, that productivity is low due to a low film formation rate and that complex and expensive high frequency generator and vacuum device are required in the plasma CVD method. Therefore, further improvements in these CVD methods have been waited.
As for the raw material, since gaseous silicon hydride which is highly toxic and reactive is used, it is difficult to handle, and a sealable vacuum device is required since the raw material is in gaseous form. In general, these devices are large and expensive and also cause an increase in production costs since they consume a large amount of energy for a vacuum system or a plasma system.
Meanwhile, in recent years, a method of coating liquid silicon hydride without using the vacuum system has been proposed. JP-A 1-29661 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses a method of forming a silicon-based thin film by causing a gaseous raw material to liquefy and adsorb on a cooled substrate and react with chemically active atomic hydrogen. However, this method has problems that a complex device is required since gasification and cooling of silicon hydride as the raw material are carried out successively and that it is difficult to control the thickness of the film.
Further, JP-A 7-267621 discloses a method of coating low-molecular-weight liquid silicon hydride to a substrate. However, this method is difficult to use since the system is unstable, and since the raw material is in liquid form, it is difficult to obtain a uniform film thickness when it is coated on a substrate with a large area.
Meanwhile, an example of a solid silicon hydride polymer is reported in British Patent GB-2077710A. However, a film cannot be formed by a coating method since the polymer is insoluble in a solvent.
Further, a polysilicon film for use in a solar battery and the like is produced primarily by a method comprising the steps of forming an amorphous silicon film by the thermal CVD method (for example, J. Vac. Sci. Technology., Vol. 14, p. 1082 (1977)) using a monosilane or disilane gas as a raw material or the plasma CVD method (for example, Solid State Com., Vol. 17, p. 1193 (1975)) and then converting the amorphous silicon film into a polysilicon film by laser annealing, a hydrogen plasma treatment or other treatment. The formation of the silicon film by use of the thermal or plasma CVD method has problems that:    (1) since a gas phase reaction is used, silicon particles are produced in the gas phase and cause the contamination of equipment and/or production of foreign materials, thereby lowering a production yield,    (2) since the raw material is in gaseous form, it is difficult to form a silicon film having a uniform thickness on a substrate having an uneven surface,    (3) productivity is low due to a low film formation rate, and    (4) complex and expensive high frequency generator and vacuum device are required in the plasma CVD method. Therefore, further improvements in these CVD methods have been waited.